Take action to prevent anthrax in cattle, bison

During a 2006 anthrax outbreak, more than 800 animals died on more than 150 premises in Saskatchewan and Manitoba. | File photo

A good time to write about anthrax is when there isn’t a big outbreak across Western Canada.

Anthrax strikes fear into most cattle producers but with the last big outbreak occurring seven years ago in 2006, there is a risk of becoming complacent.

In 2006, we learned a lot about the disease and how to control it.

Cattle are susceptible, as are other species including bison and horses.

It is considered a zoonosis, which means humans can contract it. Fortunately, in humans it is usually the cutaneous (skin) form and responds well to antibiotics.

Humans rarely get the fatal inhalation form.

In the last large outbreak, with hundreds of producers and veterinarians exposed to anthrax, only two contracted the skin form and required treatment.

About 20-25 outbreaks have been reported in cattle across Canada since 1967, but none were as significant as the 2006 outbreak in Sask-atchewan and Manitoba, where more than 800 animals died on more than 150 premises.

Cattle contact the spores from the soil. The spores can remain infective for 250 years if buried deep.

Spores on the soil surface break down over a few years, however.

Soils that are high in organic material, calcium and have a lower pH make spore survival more favour-able.

These favourable soil conditions make it easier to predict where outbreaks might occur.

Outbreaks occur primarily in two environments: a wet spring followed by a very hot, dry summer, or in very dry conditions.

In wet springs, moisture brings the spores to the surface where grazing animals gain access.

In dry years, livestock access the spores as they graze low areas close to the ground.

If enough spores are ingested , the resulting toxemia leads to severe weakness, lack of co-ordination and depression followed by quick death.

All sudden deaths in cattle or other species should be autopsied by a veterinarian to determine if the cause is anthrax, which would alert the infected herd owner and those nearby to start a preventive program.

Mature cattle that suddenly die qualify for funding under the BSE program.

Signs of anthrax in an autopsy are blood failing to clot, lack of rigor mortis to the carcass and a greatly en-larged spleen.

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Ideally, if anthrax is suspected the carcass should not be opened. The diagnosis can be made from collecting a few drops of blood.

However, here are many causes of sudden death and often anthrax is not the first disease a veterinarian suspects.

In most cases, the carcass is opened before anthrax is suspected

Lab tests are required to confirm it.

Officials will then quarantine the carcass and dispose of it.

It is best to completely burn the carcasses where the animal died. Moving carcasses spreads the spores.

Spraying the carcass with formaldehyde to prevent scavenging by predators and burying it with lime are also accepted procedures.

Keep farm dogs, cats and humans away from the carcass.

Anthrax is a reportable disease to the Canadian Food Inspection Agency but rules have greatly changed since April 1, 2013.

At that point, CFIA ended its role in anthrax prevention, diagnosis, treatment and disposal, leaving it up to veterinarians to help in the diagnosis.

The CFIA had the U.S. military quick tests for diagnosis and I hope these tests will be made available through the chief provincial veterinarians to private veterinarians in endemic areas.

The CFIA website gives recommendations on disinfection or disposal.

But prevention is the best strategy.

Geographically, anthrax appears limited to the region from Alberta through to western Ontario. In those areas, veterinarians must remain vigilant.

Local veterinarians will know where cases have been reported and whether vaccination is advisable.

The preventive vaccine is a non-encapsulated live spore vaccine.

It is called the anthrax spore vaccine (sterne 34F2 strain) and is manufactured by the Colorado Serum Company in the U.S.

The vaccine is almost 100 percent protective after giving two shots, three to four weeks apart.

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These must be boostered yearly to maintain immunity, preferably just before summer, the prime time for contraction.

The CFIA website states that the vaccine provides immunity for about one year, but it is best to give just before expected exposure.

The cost is comparable to other vaccines. It’s cheap, effective insurance.

It is administered subcutaneously and withdrawal times before slaughter in cattle is 42 days.

Antibiotics should not be administered during the eight days immediately before or after anthrax vaccination because they interfere with the development of post-vaccination immunity.

If the disease is diagnosed, the best plan is to move the cattle as quickly as possible off the contaminated area and either vaccinate or first treat with long acting penicillin, wait eight days, and then vaccinate.

Vaccination will provide some protection in as soon as seven days with total protection by 14 days after administration.

The vaccine’s label does not in-clude bison but it is protective. A prescription is needed because it is an off-label use.

Vaccination in bison is complicated by May calving. A U.S. bison veterinarian found that vaccinating in mid winter worked if the dose was doubled, providing longer protection.

It appears that the vaccine if administered to bison during fall or winter processing will offer some protection the following summer.

I’d recommend vaccination if a herd of cattle or bison was diagnosed in your immediate area, especially if on the same water course.

In the 2006 Saskatchewan outbreak, Dr. Greg Douglas, a veterinarian with the CFIA recommended vaccinating all cattle, horses, sheep, goats and bison within a five mile radius of all positive cases.

This is wise advice.

Anthrax is not part of most routine preventive programs, but if cattle are pastured in areas with a history of anthrax I would vaccinate indefinitely.

On the other hand, if there has never been a case in your immediate area, there is probably no need to vaccinate.

It is possible for anthrax to travel in purchased feed, such as round bales made in old lake bottoms during a drought when dirt spores were wound into the bales.

If sourcing your feed from a confirmed anthrax area, it would be another good reason to vaccinate.

The individual animal costs of valuable purebreds may make the decision to vaccinate easier.

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Discuss all vaccination requirements with the herd veterinarian and hopefully this dreaded disease can be held in check across Western Canada.

Roy Lewis works as a technical services veterinarian part time with Merck Animal Health in Alberta.

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